JP2000089678A - Heat-shrinkable label and label-coated plastic container - Google Patents

Abstract

(57) [Problem] To provide a heat-shrinkable label and a container having low-temperature shrinkage and excellent recyclability. SOLUTION: A heat-shrinkable film characterized in that at least one layer is printed with a foaming ink on a heat-shrinkable film obtained by stretching a styrene-based resin at least uniaxially, and the specific gravity after printing is less than 1.0. label.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable label which is printed and then heat-shrink-coated, and a container which is heat-shrink-coated with the label.

[0002]

BACKGROUND OF THE INVENTION Polyvinyl chloride (PVC) is the best known material for heat shrinkable films used in shrink labels for plastic containers. this is,
This is because the heat-shrinkable film made of PVC satisfies the user's requirements relatively widely, including practical properties such as mechanical strength, rigidity, optical properties, shrinkage properties, and cost. However, since PVC has a problem of waste treatment accompanying hydrogen chloride gas generated at the time of combustion after disposal, a heat-shrinkable film made of a material other than PVC has been demanded.

[0003] In response to this situation, styrene (PS) resins such as styrene-butadiene block copolymer,
A heat-shrinkable film made of polyethylene terephthalate (PET) -based resin has been developed and has begun to be widely used as a label.

However, in particular, when used in a container made of plastic having a specific gravity of 1.0 or more, such as a PET bottle, a problem has been pointed out from the viewpoint of reusing (recycling). That is, in recycling the container itself, as a method of selecting other materials such as a label, separation is performed by crushing the container and then in water due to a difference in specific gravity. However, since the specific gravity of the PS-based and PET-based shrink films exceeds 1.0, the specific gravity cannot be separated from the material of the container body.

Japanese Patent Application Laid-Open No. 61-25834 proposes a laminated film of a foamed layer and a non-foamed layer for the purpose of improving chemical resistance and the like. It is not preferable from the viewpoint of low-temperature shrinkage in the sense of causing. A polystyrene foam sheet having improved low-temperature shrinkability is disclosed in JP-A-62-27439.
In Japanese Patent Laid-Open Publication No. HEI 9-204, a foamed sheet using a styrene-acrylic copolymer has been proposed. Although this sheet is excellent in low-temperature shrinkability, it is an opaque sheet and cannot be used for back printing which is usually performed on labels. Furthermore, the expansion ratio was too high, and there was a problem in rigidity and mechanical strength.

[0006]

SUMMARY OF THE INVENTION The present invention has found a heat-shrinkable label which can solve the above-mentioned problems, and the gist of the present invention is that the Vicat softening point is 60 to 95 ° C.
A heat-shrinkable label characterized in that at least one layer is printed with a foaming ink on a heat-shrinkable film obtained by stretching a styrene-based resin at least uniaxially, and the specific gravity after printing is less than 1.0. Yes, the styrene-based resin is preferably made of a styrene-butadiene block copolymer and / or a rubber-reinforced styrene-acrylic copolymer, and has a shrinkage ratio when immersed in hot water of 80 ° C. for 10 seconds. It is preferably 10% or more in at least one direction, and furthermore, a plastic container having a specific gravity of 1.0 or more obtained by coating these heat shrink labels with heat shrink is provided.

[0007]

Hereinafter, the present invention will be described in detail. The polystyrene-based resin used in the present invention is selected mainly from a styrene-butadiene block copolymer and a rubber-reinforced styrene-acrylic copolymer, and may be a substantially rubber-reinforced transparent polystyrene-based resin and a composition. Can be widely used. Examples of these include ethylene-styrene block copolymer, styrene-
Isoprene block copolymer (SIS), hydrogenated styrene-butadiene block copolymer (SEBS), hydrogenated styrene-isoprene block copolymer (SEPS), acrylonitrile-butadiene-styrene block copolymer (ABS), etc. Is a mixture of the above resin and a general-purpose polystyrene resin (GPPS).

The structure of the styrene-butadiene block copolymer is not particularly limited as long as it is a block copolymer having a polystyrene segment and polybutadiene. The structure of the entire block copolymer includes, for example, a linear type and a star type. The structure of each block segment includes, for example, a completely symmetric block, an asymmetric block, a tetra block, a tapered block, and a random block. Further, two or more types of block copolymers having different copolymer composition ratios, block copolymer structures, structures of respective block portions, molecular weights, and polymerization methods may be blended. Commercial products include "Asaflex" manufactured by Asahi Kasei Kogyo Co., Ltd., "Clearen" manufactured by Denki Kagaku Kogyo Co., Ltd., "K-Resin" manufactured by Philips Oil, BASF
And "Finaclear" manufactured by FINA.

The rubber-reinforced styrene-acrylic copolymer is a resin obtained by dispersing styrene-butadiene rubber particles having a surface graft polymerized and having a refractive index matched with that of a matrix in a styrene / acrylic acid monomer copolymer matrix. Is mentioned. Examples of commercially available products include “Polystyrene SD” manufactured by Asahi Kasei Kogyo Co., Ltd. and “Clearpact” manufactured by Dainippon Ink and Chemicals, Inc. Moreover,
Non-rubber reinforced styrene-acryl styrene copolymer (for example, "Polystyrene SC" manufactured by Asahi Kasei Corporation)
Compositions mixed with butadiene block copolymers can also be considered as rubber reinforced styrene acrylic copolymers.
Further, two or more of the above polystyrene resins may be used as a mixture.

The MFR of a polystyrene resin (200 ° C.)
5Kg) is from 0.5 to 10.0, preferably from 1.0 to
4.0 is desirable. If the MFR is less than 0.5, the productivity of the melt extrusion decreases, and if it exceeds 10.0, stretching becomes difficult.

The polystyrene resin preferably has a tensile modulus (injection dumbbell piece) of 100 to 250 kgf / mm ² . If it is less than 100 kgf / mm ² ,
The required rigidity of the shrink film is hardly obtained, and the workability in the secondary processing step is reduced, and wrinkling is likely to occur in the shrink step. If it exceeds 250 kgf / mm ² , the amount of rubber is too small, and the rupture resistance of the film tends to decrease.

The preferred range of the amount of rubber is 3 to 30% by weight, more preferably 8 to 25% by weight. The rubber composition is SB
It may be copolymerized as in S, or the particles may be graft-polymerized as in rubber-reinforced styrene acrylic copolymer, and the effect may be exhibited by simple dispersion. Also,
In order to increase the elastic modulus, an inorganic filler may be added.

In the present invention, the polystyrene resin to be used is one in a polystyrene resin of a single polymer.
It is necessary that the Vicat softening point of not less than 00 ° C is 60 to 95 ° C. If it is lower than 60 ° C., so-called spontaneous shrinkage of the film during storage tends to occur, and if it exceeds 95 ° C., it is difficult to obtain low-temperature shrinkability. Here, the measuring method of the Vicat softening point is JIS-K7206 A method (1.
Kg). Natural shrinkage is generally 30 ° C x 30 days or 40 ° C x 7 depending on the application.
Days, the shrinkage is 3.0% or less, preferably 2.0%
It must be:

The Vicat softening point is adjusted by randomly (or tapered) copolymerizing a low Tg monomer with a polystyrene resin or by adding a plasticizer. Monomers randomly copolymerized with styrene include butadiene,
Conjugated dienes such as isoprene and 1,3-pentadiene,
(Meth) acrylate monomers such as methyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, and stearyl (meth) acrylate are preferably used. The following can be exemplified as the plasticizer.

Aliphatic plasticizers such as dioctyl sebacate, dioctyl adipate, diisononyl adipate and diisodecyl adipate; aromatic ester plasticizers such as diethyl phthalate, dibutyl phthalate, dioctyl phthalate, diisodecyl phthalate and dicyclohexyl phthalate; Poly (1,4-ethylene adipate), poly (1,
Aliphatic polyester-based plasticizers such as 4-ethylene succinate) or polyester ether-based plasticizers: phosphate ester-based plasticizers such as tricresyl phosphate and triphenyl phosphate.

In the styrene-butadiene block copolymer, the Vicat softening point can be lowered by increasing the compatibility between the styrene segment and the butadiene segment in addition to the random copolymerization of butadiene in the styrene segment. On the other hand, commercially available rubber-reinforced styrene acrylic copolymers (eg, "SD" manufactured by Asahi Kasei Kogyo Co., Ltd., "Clearpact" manufactured by Dainippon Ink Industries, Ltd.) include, in addition to the main monomers of styrene and methyl methacrylate, The use of butyl acrylate as a comonomer lowers the Vicat softening point.

The polystyrene-based resin selected from one or more of the above contents is melt-extruded into a film using an extruder. A plurality of raw materials and additives may be compounded in advance using a twin-screw extruder, or may be dry-blended during film extrusion. The extruded film is stretched by an inflation method, a tubular method, a tenter method, or the like. The stretching temperature is generally in the range from the Vicat softening point to the Vicat softening point + 30 ° C., and the stretching ratio is at least 1.2 to 10.0 times, preferably 1.5 to 7.5 times, and more preferably 2 times in one direction. 0.0-5.
It is determined in a range of 5 times. The stretching method most preferably recommended from the viewpoint of productivity, appearance accuracy, and shrinkage control is a sequential biaxial stretching method using a tenter.

In a heat-shrinkable film, the shrinkage when immersed in warm water at 80 ° C. for 10 seconds has a shrinkage of at least 10 in one direction.
% Or less, and less than 10%, it is difficult to obtain a tight feeling after shrinkage, although depending on the shape, when coated on a plastic container.

The thickness of the film after stretching varies depending on the use and the like, but is 10 to 500 μm, preferably 20 to 100 μm.
Adjusted in μm. The heat-shrinkable film formed and processed as described above is subjected to printing and bag-making processing to be processed into a heat-shrinkable label.

In the present invention, in the printing step, it is important to print at least one layer with foamed ink. Foaming ink is an ink that foams by heat, and usually contains a low boiling point solvent such as hexane in heat-expandable microcapsules, and the volume of the microcapsules expands tens to hundreds times by heating. It is.

Printing is usually performed in several layers for each color, and the foamed ink is used for at least one of the layers. From the viewpoint of maintaining the printing area and flatness, it is preferably used for the final solid white layer. For printing, any method such as screen, gravure, offset, and silk can be used. The foamed ink is hardly foamed immediately after printing, but is foamed by subsequent heating by hot air, steam, infrared rays, electromagnetic waves, friction, or the like. The heat may be applied when the heat-shrinkable label is shrink-coated on the plastic container so as to be foamed.

The amount of ink per film area and the expansion ratio are appropriately determined according to the specific gravity of the printed label. It is most important that the specific gravity of the label be 1.0 or less in the present invention. The specific gravity of the styrene resin is approximately 1.01 to
1.07, but the specific gravity of the label after printing the foaming ink and performing the foaming treatment must be 1.0 or less. PV
For heat-shrinkable labels such as C and PET, the specific gravity of the base film is too large, 1.30 or more. Even if foamed ink is used, the specific gravity is reduced to 1.0 or less while maintaining flatness and workability. Can not. If the base film is a foam film, the specific gravity can be easily reduced, but there is a problem that back printing cannot be performed due to lack of transparency. As described above, the heat-shrinkable label subjected to bag making after printing has a specific gravity of 1.
Covered with zero or more plastic containers. Specific gravity is 1.0
Examples of the above plastics include polyester resins such as polyethylene terephthalate, polystyrene resins, polycarbonate resins, nylon resins, polyvinyl chloride, phenol resins, and melamine resins. In addition, examples of the form of the plastic container include a bottle, a tray, a lunch box, a side dish container, and a dairy product container.

[0023]

The present invention is not limited by the following examples. In addition, the measurement value and evaluation shown in an Example were performed as follows. Here, the film taking (flow) direction is MD, and the orthogonal direction is TD.
It is described.

1) Vicat softening point Using an injection test piece of a raw material resin, JIS-K7206A
It was measured in accordance with the method (1 kg).

2) Specific Gravity A label is cut out to 2 mm × 7 mm, and JIS-K711
In accordance with No. 2, the measurement was performed by the floatation / sinking method.

3) Thermal Shrinkage The film was cut into a size of 100 mm in MD and 100 mm in TD, immersed in a hot water bath at 80 ° C. for 10 seconds, and the amount of thermal shrinkage of TD was measured. As for the heat shrinkage, the ratio of the amount of shrinkage to the original size before shrinkage was expressed as a percentage value.

4) Natural Shrinkage Rate The film was cut into a size of 50 mm in MD and 1000 mm in TD, and allowed to stand in a thermostat at 40 ° C. for 1 week, after which the TD shrinkage was measured. As for the heat shrinkage, the ratio of the amount of shrinkage to the original size before shrinkage was expressed as a percentage value.

5) Recyclability A preweighed plastic container coated with a heat-shrinkable label was put into a Rotoplex crusher manufactured by Hosokawa Micron Corporation and crushed into flakes having a size of about 5 to 20 mm ² . All the flakes were scraped, poured into 200 liters of water, stirred for 5 minutes, allowed to stand for 1 minute, then the floating flakes were scooped, dried and weighed, and the recovery rate was calculated in%.

Examples 1 and 2 / Comparative Examples 1 and 2 A polystyrene "SS-700" (SD series) manufactured by Asahi Kasei Kogyo Co., Ltd. having a Vicat softening point of 78.degree. (Manufactured by Heavy Industries, Ltd.) at an extrusion temperature of 20
Melt extrusion was performed from a T-die set at 0 ° C. After a while
T at 92 ° C using a film tenter manufactured by Mitsubishi Heavy Industries, Ltd.
D was stretched three times. The stretched film had a thickness of 50 μm, a specific gravity of 1.10, a heat shrinkage of 45%, and a natural shrinkage of 0.3%.

The film was subjected to solid gravure printing (back printing) using “New Die Form S-801” manufactured by Dainichi Seika Kogyo Co., Ltd., which is a foaming ink, to obtain a folded diameter of 140 mm × length of 100 mm. The bag was made and used as a label. New diform was used after diluting 1.5 times with a solution of ethyl acetate / toluene / isopropyl alcohol = 3/1/6. As a printing machine, "GRAVO-PROOF MULTI" manufactured by Nissho Gravure Co., Ltd. was used.
The thickness of the ink layer after printing was 5 μm. This label is attached to a round PET bottle (1.5 liter capacity)
The sheet was passed through a steam oven at 100 ° C. for 30 seconds to shrink and cover the label, and at the same time, foamed the ink. The specific gravity of the entire label after the foaming treatment was measured.

Further, the temperature of the steam furnace was changed and the expansion ratio was changed. Furthermore, “Shrink Pack PS-98” manufactured by Sakata Inx which is a non-foaming ink.
Using "5", a similar study was conducted. The above measurements,
Table 1 shows the evaluation results.

[0032]

[Table 1]

From Table 1, it can be seen that Examples 1 and 2 in which the specific gravity of the printed label was less than 1.0 using the foamed ink of the present invention were excellent in heat shrinkability and recyclability. On the other hand, it can be seen that Comparative Examples 1 and 2 in which the label specific gravity after printing is too large are inferior in recyclability.

Examples 3 and 4 Comparative Examples 3 and 4 As a styrene resin, "K Resin KR-" manufactured by Philips Sekiyu KK
10 "and" GPPS HH-102 "manufactured by Mitsubishi Chemical Corporation.
Using (KR-10 / HH-102 = 70/30), a plasticizer-free plasticizer and a plasticizer containing dioctyl phthalate (DOP) with a different amount of addition are used in the same manner as described above. The film was made with. The film was printed using the foamed inks of Examples 1 and 2 in the same manner, and then the specific gravity of the entire label after the foaming treatment was measured. Further, evaluation was performed in the same manner as described above. The results are shown in Table 2.

[0035]

[Table 2]

As shown in Table 2, the heat-shrinkable film and the foamed ink of the present invention have excellent heat-shrinkability and recyclability for Examples 1 and 2 in which the specific gravity of the printed label is less than 1.0. I understand. On the other hand, Comparative Example 3 using a heat-shrinkable film having an excessively high Vicat softening point is excellent in recyclability, but inferior in heat-shrinkability and Comparative Example 4 using a heat-shrinkable film having an excessively low Vicat softening point. It turns out that the natural shrinkage is inferior.

[0037]

According to the present invention, it is possible to obtain a heat-shrinkable label and a container having a low-temperature shrinkage property and particularly having excellent recyclability.

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (reference) B29L 9:00 F term (reference) 4F100 AK01C AK15A AK15J AK25A AK25J AK73A AL01A AL02A AL05A AN00A BA02 BA03 BA10A BA10B BA10C BA13 CC00B DJ01B GB90 HB31B JA03 JA04A JA13 JA13C YY00 YY00A YY00C 4F210 AA13 AH55 QA02 QC03 QG01 QG12 QG15 QG18 RA03 RC02 RG04 RG23 RG27 RG43

Claims (4)

[Claims] 1. A heat-shrinkable film obtained by stretching a styrene-based resin having a Vicat softening point of 60 to 95 ° C. at least uniaxially, printing at least one layer with a foamed ink, and having a specific gravity of 1.0 after printing. A heat-shrinkable label. 2. The heat-shrinkable label according to claim 1, wherein the styrene resin comprises a styrene-butadiene block copolymer and / or a rubber-reinforced styrene-acryl copolymer. 3. The heat-shrinkable label according to claim 1, wherein a shrinkage ratio when immersed in hot water at 80 ° C. for 10 seconds is 10% or more in at least one direction. 4. A container made of plastic having a specific gravity of 1.0 or more, wherein the label according to claim 1 is heat-shrink-coated.